Mechanisms of Neurodegeneration in CMT4B3: a Complex Pediatric Neurodevelopmental Disorder

腓骨肌萎缩症4 B3型（CMT 4 B3）是一种罕见的常染色体隐性遗传病， 轴突神经病，通常在婴儿期表现为发育里程碑的严重退化 或童年早期。CMT 4 B3具有广泛的临床症状谱。它从一个孤立的 脱髓鞘感觉运动性多发性神经病转变为复杂的神经发育表型，伴有轴突 神经病变、颅神经受累、智力残疾和面部畸形。大多数孩子 受CMT 4 B3影响的患者表现为严重表型。CMT 4 B3是由Sbf 1基因突变引起的。 基因，导致假肌醇磷酸酶，肌管蛋白相关蛋白的功能破坏 5（MTMR 5）。在这个建议中，我们专注于MTMR 5，一个发育中重要的自噬调节因子 和内-溶酶体运输，以及其参与适当的轴突稳态。 已知MTMR 5催化调节和支配肌管蛋白的亚细胞定位。 相关蛋白2（MTMR 2），一种抗磷脂酰肌醇类的活性磷酸酶。MTMR 2具有 已知在雪旺细胞稳态中的作用，MTMR 2的缺失导致脱髓鞘性神经病。 MTMR 5也被鉴定为神经元特异性自噬抑制因子。尽管有这些知识， 目前还完全不清楚MTMR 5的功能被破坏是如何导致早期轴突变性的。 童年.通过这项奖学金的目的，并使用已建立的iPSC衍生的运动神经元， CMT 4 B3的模型，我试图阐明MTMR 5在运动神经元中的生化作用，以及MTMR 5的丢失如何影响运动神经元的功能。 正常的MTMR 5功能导致发育早期的轴突变性。在本奖学金的目标1中， 我建议利用CMT 4 B3的iPSC衍生的运动神经元模型来理解 MTMR 2、MTMR 13和磷酸肌醇水平上的MTMR 5损失，并区分是否存在残留MTMR 5 功能导致轴突中毒。在目标2中，我试图用基因表达谱来表征 由于MTMR 5丢失导致的下游缺陷，这可能源于MTMR 5在自噬中的作用， 溶酶体内运输我计划开发高内涵的基于图像的分析， 分析结果，并为药物发现和基因治疗验证创建急需的平台。 充分理解CMT 4 B3的机制对NICHD的使命至关重要。等 知识对于开发和适当评估治疗方式至关重要， CMT 4 B3患者。从这个角度来看，拟议的项目是针对我的培训， 成为一名儿科神经学家和科学家。

Charcot-Marie-Tooth Disease type 4B3 (CMT4B3) is a rare, autosomal recessive hereditary axonal neuropathy, often presenting with severe regression of developmental milestones during infancy or early childhood. CMT4B3 has a wide clinical spectrum of symptoms. It ranges from an isolated demyelinating sensorimotor polyneuropathy to a complex neurodevelopmental phenotype with axonal neuropathy, cranial nerve involvement, intellectual disability and facial dysmorphism. Most children affected by CMT4B3 present with the severe phenotype. CMT4B3 is caused by mutations in the Sbf1 gene, resulting in disrupted function of the pseudo-inositol phosphatase, Myotubularin-Related Protein 5 (MTMR5). In this proposal, we focus on MTMR5, a developmentally important regulator of autophagy and endo-lysosomal trafficking, and its involvement in proper axonal homeostasis. MTMR5 is known to catalytically regulate and dictate the subcellular localization of Myotubularin- Related Protein 2 (MTMR2), an active phosphatase against phosphatidylinositol species. MTMR2 has known roles in Schwann cell homeostasis and loss of MTMR2 leads to a demyelinating neuropathy. MTMR5 was also identified as a neuron-specific suppressor of autophagy. Despite this knowledge, it is entirely unknown how disrupted function of MTMR5 leads to axonal degeneration during early childhood. Through the aims of this fellowship and using an established iPSC-derived motor neuron model of CMT4B3, I seek to clarify the biochemical role of MTMR5 in motor neurons and how loss of normal MTMR5 function results in axon degeneration early in development. In Aim 1 of this fellowship, I propose to utilize an iPSC-derived motor neuron model of CMT4B3 to understand the effects of MTMR5 loss on MTMR2, MTMR13, and phosphoinositide levels and discriminate if residual MTMR5 function causes toxicity in axons. In Aim 2, I seek to l gene expression profiling to characterize the downstream defects as a result of MTMR5 loss, which likely stem from MTMR5’s role in autophagy and endo-lysosomal trafficking. I plan to develop high-content image-based analyses to confirm expression profiling results and to create a much needed platform for drug discovery and gene therapy validation. Fully understanding the mechanisms underlying CMT4B3 is critical to the NICHD mission. Such knowledge is crucial for development and proper evaluation of therapeutic modalities that could help CMT4B3 patients. With this perspective, the proposed project is tailored to my training towards becoming a translational pediatric neurologist and scientist.